Well flushing fluid suitable for heavy oil deposition of oil field shaft as well as preparation method and application of well flushing fluid

Abstract

The invention relates to the technical field of oilfield chemistry, in particular to flushing fluid suitable for heavy oil deposition of an oilfield shaft and a preparation method and application of the flushing fluid. The flushing fluid suitable for heavy oil deposition in the shaft of the oil field is prepared from the following raw materials in percentage by weight: 3%-5% of an organic solvent, 10%-12% of a sodium silicate aqueous solution, 0.05%-0.15% of sodium chloride, 0.25%-0.5% of a surfactant, 0.25%-0.5% of an auxiliary agent and the balance of water. The well washing fluid can be used in well washing operation, extra heating equipment is not needed on an oil field site, a good washing effect can be achieved only through self-heating in a well, low-temperature washing is achieved, the oil washing efficiency on the inner wall of a casing pipe can reach 95% or above after 30 min, a solution system obtained after washing can achieve rapid oil-water separation on the ground, the separation time is shorter than 10 min, and the well washing fluid is suitable for being used for well washing. And heavy oil recovery is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, and in particular to a well-washing fluid suitable for thick oil deposition in oilfield wellbores, and a preparation method and application thereof. Background Art

[0002] Heavy oil refers to crude oil with high viscosity and poor fluidity. It contains high content of colloid, asphaltene and wax and has low freezing point. During the mining process, the temperature often drops, causing the heavy oil to deposit and adhere to the casing wall and drilling tools and be difficult to clean. This situation seriously affects the normal operation and production efficiency of the equipment. Heavy oil well washing fluid is a key chemical used in the petroleum industry to clean oil pipelines, crude oil storage tanks, casing walls and other equipment. Traditional heavy oil well washing fluids often have problems such as poor permeability and unsatisfactory oil washing effects, and require higher temperatures (usually 50-80°C) during the cleaning process, which not only wastes energy, but also increases construction risks and costs.

[0003] In recent years, the research and development direction of heavy oil well-washing fluids has gradually turned to low temperature, environmental protection, and rapid separation of oil and water on the ground. Although some heavy oil well-washing fluids based on surfactants have improved the cleaning effect to a certain extent, their preparation process is complicated and requires a higher temperature (80°C), and they cannot achieve rapid separation of the well-washing fluid on the ground. Instead, they exist in the form of emulsions, which is difficult to meet the needs of low-temperature and efficient cleaning. In addition, these well-washing fluids often require the use of specific surfactants, which are not only expensive, but also pollute the environment to a certain extent. At present, there are also heavy oil well-washing fluids based on organic solvents, but they all contain aromatic hydrocarbons, such as xylene, which are extremely toxic to the human body and pollute the environment. In addition, such organic solvents are costly and have low economic benefits.

[0004] At present, there are some heavy oil well washing fluid products on the market, but these products generally have the following problems: (1) Poor permeability: Due to the high viscosity of heavy oil, traditional well washing fluids are difficult to penetrate into the heavy oil, resulting in poor cleaning effect; (2) Low oil washing efficiency: Even under high temperature conditions, the cleaning effect of traditional well washing fluid on heavy oil is still not ideal, and multiple washings are required to achieve satisfactory results; (3) High energy consumption: Since cleaning needs to be done at a higher temperature, a lot of energy is consumed; (4) Environmental pollution: Some well washing fluids will generate harmful wastewater and waste gas during production and use. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a well-washing fluid suitable for thick oil deposits in oilfield wellbores, a preparation method and an application thereof. The well-washing fluid is prepared with organic solvents, sodium silicate aqueous solution and surfactant as main raw materials, and the well-washing fluid can quickly separate oil and water on the ground, has good permeability, high oil washing efficiency, does not solidify at low temperatures, has low energy consumption and is environmentally friendly.

[0006] The well washing fluid suitable for thick oil deposits in oilfield wellbores of the present invention is composed of the following raw materials by weight percentage: 3% to 5% organic solvent, 10% to 12% sodium silicate aqueous solution, 0.05% to 0.15% sodium chloride, 0.25% to 0.5% surfactant, 0.25% to 0.5% additive, and the balance water.

[0007] The organic solvent is n-dodecane or n-tetradecane or isomeric tetradecane or n-hexadecane or white oil. Organic solvents are key components of well washing fluids, of which n-tetradecane and white oil are the two most effective. The reasons for selecting the above organic solvents are environmental protection, effectiveness at low temperatures (reducing construction costs and difficulties, no ground heating equipment is required, only self-heating in the well can achieve the effect, and the wellhead temperature is generally 35-40°C), and rapid separation of heavy oil on the ground for easy recovery. Both n-tetradecane and white oil are non-toxic and odorless environmentally friendly organic solvents, and do not have the flammability of gasoline, kerosene, etc. Heavy oil is mainly composed of high molecular weight alkanes, cycloalkanes and aromatics, with complex chemical structures and strong intermolecular forces. Straight-chain alkanes such as n-tetradecane have high lipophilicity and can effectively dissolve long-chain alkanes and non-polar components in heavy oil. Due to the principle of "like dissolves like", straight-chain alkane molecules have good compatibility with non-polar components in heavy oil, so that heavy oil can be dissolved more efficiently. Straight-chain alkanes are more flexible than branched or cyclic carbon atoms, and their molecules are more densely packed, which helps them penetrate into the interior of heavy oil and destroy its intermolecular forces. With the assistance of appropriate surfactants, straight-chain alkanes are more likely to form stable oil-water emulsions, promote the emulsification and dispersion of heavy oil, and improve washing efficiency.

[0008] Straight-chain alkanes can reduce the interfacial tension between heavy oil and solid surface, thus helping heavy oil to detach from the surface. Straight-chain alkanes are more flexible than branched or cyclic alkanes, and their molecules are more tightly packed, thus helping them to penetrate into the heavy oil and destroy its intermolecular forces.

[0009] In terms of mass ratio, organic solvent: sodium silicate aqueous solution = 1:2~1:4.

[0010] The modulus of sodium silicate is greater than 2, preferably 3.2, the mass fraction of sodium silicate aqueous solution is 40%, the solution is relatively thin, the viscosity is low, and the fluidity is good. If the modulus is too small, the fluidity will be poor, and the pumping and circulation well washing operations cannot be achieved; if the modulus is too large, it cannot effectively reduce the viscosity of heavy oil.

[0011] The present invention uses a sodium silicate aqueous solution, and the sodium ions (Na + ) can interact with the molecules in the oil to a certain extent, reduce the mutual attraction between the oil molecules, improve the oil-water interfacial tension, thereby reducing the viscosity of the heavy oil and improving the permeability. Moreover, the sodium silicate aqueous solution is an alkaline substance, which can significantly increase the pH value of the aqueous solution. Under high pH conditions, some acidic components in the heavy oil (such as natural fatty acids) will be converted into anionic surfactants, enhancing the emulsification of the oil-water interface, while also being able to destroy the strong interfacial adsorption between the heavy oil and the solid surface, and promoting the dissociation between the heavy oil molecules.

[0012] Adding trace amounts of sodium chloride can effectively increase the interfacial tension between oil and water, thereby achieving the purpose of rapid oil-water separation. Due to the ion shielding effect, sodium chloride dissociates into sodium ions (Na + ) and chloride ions (Cl - ). These ions are distributed in the water phase and form an electrical double layer near the oil-water interface, limiting the direct interaction between the oil phase molecules and the water phase molecules. In addition, the sodium chloride ions will competitively adsorb on the water phase interface, replacing the positions of some surfactant molecules, weakening the ability of surfactants to reduce interfacial tension. For systems containing natural surfactants (such as colloids and asphaltene in heavy oil), sodium chloride will inhibit their adsorption on the interface, causing the interfacial tension to rise again.

[0013] The auxiliary agent is Span-80 or polysorbate-80 or lecithin or lauric acid.

[0014] The surfactant is sodium dodecyl sulfate or sodium dodecyl sulfonate or monostearate glyceryl or dioctyl sodium sulfosuccinate.

[0015] The preparation method of the well washing fluid suitable for thick oil deposition in oilfield wellbore of the present invention comprises the following steps: weighing various raw materials in proportion, mixing, stirring for 30 minutes at room temperature until the mixture is uniform and transparent, and obtaining a finished product. The stirring speed is 60 r / min, and the preferred order of adding materials is water, surfactant, sodium chloride, sodium silicate aqueous solution, organic solvent, and additive.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The well-washing fluid of the present invention reduces construction costs and difficulty. No additional heating equipment is required at the oil field site. Good cleaning effects can be achieved by self-heating in the well, thus achieving low-temperature cleaning and reducing the risk of well-washing operations, thereby reducing both costs and energy consumption. (2) The well-washing fluid of the present invention has good penetration and cleaning ability for heavy oil, and can be used for cleaning casing and drilling tools of heavy oil wells. Conventional well-washing fluids usually require a long period of circulation to achieve a cleaning efficiency of 90%. The present invention can achieve an oil washing efficiency of more than 95% on the inner wall of the casing in an environment of 35°C in just 30 minutes, and can reach a maximum of 99%; (3) The raw materials of the well-washing fluid of the present invention are cheap, easy to obtain, environmentally friendly, non-toxic, odorless, and not flammable or explosive, which greatly reduces the cost of well-washing operations and improves the safety of well-washing operations; (4) The solution system after the well washing fluid of the present invention is used can realize rapid oil-water separation on the ground, and the separation time is less than 10 minutes. After the oil phase and the water phase are quickly separated, the heavy oil exists in the organic solvent, which is conducive to the recovery of the washed heavy oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a diagram of the cleaning effect of the well-washing fluid of the present invention, in which A is a hollow steel column before cleaning, B is the well-washing fluid before cleaning, C is a hollow steel column after cleaning, D is a hollow steel column after cleaning and rinsing with clean water for 1 second, and E is a solution system after cleaning is completed; Figure 2 This is a diagram of the cleaning effect of the well washing fluid in Comparative Example 1. In the figure, A is a hollow steel column before cleaning, B is the well washing fluid before cleaning, C is a hollow steel column after cleaning, and D is a solution system after cleaning. DETAILED DESCRIPTION

[0018] Example 1 Well-washing fluid suitable for heavy oil deposits in oilfield wellbores, composed of the following raw materials in percentage by weight: Organic solvent 3% Sodium silicate aqueous solution 10% Sodium chloride 0.05% Surfactant 0.25% Additives 0.25% Water 86.4% The organic solvent is n-dodecane, the surfactant is sodium dodecyl sulfonate, the auxiliary agent is Span-80, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0019] Preparation method: Pour 86.4 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.25 parts of surfactant, 0.05 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0020] Example 2 Well-washing fluid suitable for heavy oil deposits in oilfield wellbores, composed of the following raw materials in percentage by weight: Organic solvent 4% Sodium silicate aqueous solution 11% Sodium chloride 0.05% Surfactant 0.5% Additives 0.3% Water 85.1% The organic solvent is isomeric tetradecane, the surfactant is dioctyl sodium sulfosuccinate, the auxiliary agent is lecithin, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0021] Preparation method: Pour 85.1 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.5 parts of surfactant, 0.05 parts of sodium chloride, 11 parts of sodium silicate aqueous solution, 4 parts of organic solvent, and 0.3 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0022] Example 3 Well-washing fluid suitable for heavy oil deposits in oilfield wellbores, composed of the following raw materials in percentage by weight: Organic solvent 5% Sodium silicate aqueous solution 12% Sodium chloride 0.15% Surfactant 0.5% Additives 0.5% Water 83.4% The organic solvent is n-hexadecane, the surfactant is monostearate glyceryl, the auxiliary agent is lauric acid, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0023] Preparation method: Pour 83.4 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.5 parts of surfactant, 0.15 parts of sodium chloride, 12 parts of sodium silicate aqueous solution, 5 parts of organic solvent, and 0.5 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0024] Example 4 Well-washing fluid suitable for heavy oil deposits in oilfield wellbores, composed of the following raw materials in percentage by weight: Organic solvent 3% Sodium silicate aqueous solution 10% Sodium chloride 0.1% Surfactant 0.25% Additives 0.25% Water 86.4% The organic solvent is white oil, the surfactant is sodium dodecyl sulfate, the additive is polysorbate 80, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0025] Preparation method: Pour 86.4 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0026] Example 5 Well-washing fluid suitable for heavy oil deposits in oilfield wellbores, composed of the following raw materials in percentage by weight: Organic solvent 3% Sodium silicate aqueous solution 10% Sodium chloride 0.1% Surfactant 0.25% Additives 0.25% Water 86.4% The organic solvent is n-tetradecane, the surfactant is sodium dodecyl sulfate, the auxiliary agent is polysorbate-80, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0027] Preparation method: Pour 86.4 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0028] Comparative Example 1 The heavy oil washing fluid is composed of the following raw materials in terms of weight percentage: Sodium silicate aqueous solution 10% Sodium chloride 0.1% Surfactant 0.25% Additives 0.25% Water 89.4% There is no organic solvent, the surfactant is sodium dodecyl sulfate, the auxiliary agent is polysorbate-80, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0029] Preparation method: Pour 89.4 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, and 0.25 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0030] Comparative Example 2 The heavy oil washing fluid is composed of the following raw materials in terms of weight percentage: Organic solvent 3% Sodium chloride 0.1% Surfactant 0.25% Additives 0.25% Water 96.4% The organic solvent is n-tetradecane, the surfactant is sodium dodecyl sulfate, and the auxiliary agent is polysorbate-80.

[0031] Preparation method: Pour 96.4 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.25 parts of surfactant, 0.1 parts of sodium chloride, 3 parts of organic solvent, and 0.25 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0032] Comparative Example 3 The heavy oil washing fluid is composed of the following raw materials in terms of weight percentage: Organic solvent 3% Sodium silicate aqueous solution 10% Surfactant 0.25% Additives 0.25% Water 86.5% The organic solvent is n-tetradecane, the surfactant is sodium dodecyl sulfate, the auxiliary agent is polysorbate-80, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0033] Preparation method: Pour 86.5 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.25 parts of surfactant, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0034] Comparative Example 4 The heavy oil washing fluid is composed of the following raw materials in terms of weight percentage: Organic solvent 3% Sodium silicate aqueous solution 10% Sodium chloride 0.1% Additives 0.25% Water 86.65% The organic solvent is n-tetradecane, the auxiliary agent is polysorbate-80, the modulus of sodium silicate is 3.2, and the mass fraction of the sodium silicate aqueous solution is 40%.

[0035] Preparation method: Pour 86.65 parts of water into a stirring container, use a constant speed magnetic stirrer to set the speed to 60 r / min, then add 0.1 parts of sodium chloride, 10 parts of sodium silicate aqueous solution, 3 parts of organic solvent, and 0.25 parts of auxiliary agent to the stirring container in sequence, stir at room temperature for 30 minutes until it is uniform and transparent to obtain the finished product.

[0036] Test Case Cleaning performance determination: Experimental methods: 1. Apply heavy oil to the outer surface of a hollow steel column with a diameter of 100 mm and a wall thickness of 3 mm until no steel column surface is exposed (the viscosity of the heavy oil is greater than 2500 mPa·s, measured at 25°C); 2. Heat the prepared well-washing fluid in a water bath to 35°C, use a homemade stirring clamp to clamp the hollow steel column with heavy oil on the surface and immerse it in the well-washing fluid; 3. Turn on the agitator and set the speed to 150 r / min. After rotating and rinsing for 30 minutes, take out the clamp and steel column, remove the surface moisture, and the cleaning is completed.

[0037] The well washing fluids obtained in Examples 1-5 and Comparative Examples 1-4 were used to clean the outer surface of the steel column according to the above cleaning steps. The experimental results are as follows: .

[0038] The well washing fluid of the present invention achieves an ideal cleaning effect. At a temperature of 35°C, the cleaning efficiency exceeds 90%, and can reach up to 99%, meeting the cleaning requirements for petroleum equipment. By using the well washing fluid of the present invention, the solution system after cleaning can quickly separate the heavy oil and the aqueous solution within 10 minutes. The specific effects are as follows: Figure 1 As shown; using the well washing fluid described in Comparative Example 1, only a small part of the steel column surface is exposed after cleaning, and the specific effect of the well washing fluid solution is as follows Figure 2 As shown; using the well washing fluid described in Comparative Example 3, although the cleaning efficiency exceeds 90%, the separation time of the heavy oil and the aqueous solution is significantly prolonged.

Claims

1. A well-washing fluid suitable for heavy oil deposits in oilfield wellbores, characterized in that: In terms of weight percentage, it is composed of the following raw materials: 3% to 5% organic solvent, 10% to 12% sodium silicate aqueous solution, 0.05% to 0.15% sodium chloride, 0.25% to 0.5% surfactant, 0.25% to 0.5% additive, and the balance water; The organic solvent is n-dodecane or n-tetradecane or isomeric tetradecane or n-hexadecane or white oil; The auxiliary agent is Span-80 or polysorbate-80 or lecithin or lauric acid; The surfactant is sodium dodecyl sulfate or sodium dodecyl sulfonate or monostearate glyceryl or dioctyl sodium sulfosuccinate.

2. The well washing fluid suitable for heavy oil deposition in oil field wellbore according to claim 1, characterized in that: In terms of mass ratio, organic solvent: sodium silicate aqueous solution = 1:2~1:

4.

3. The well washing fluid suitable for heavy oil deposition in oilfield wellbore according to claim 1, characterized in that: The modulus of sodium silicate aqueous solution is greater than 2, and the mass fraction is 40%.

4. The method for preparing a well washing fluid suitable for heavy oil deposits in oil field well bores according to any one of claims 1 to 3, characterized in that: Weigh the raw materials in proportion and mix them, stir them at room temperature until they are uniform and transparent to obtain the finished product.

5. Use of the well-washing fluid suitable for heavy oil deposits in oilfield wellbores as claimed in any one of claims 1 to 3 in well-washing operations.

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